The present invention relates to a non-aqueous ball point pen ink and a ball point pen using the ink. Specifically, the present invention relates to a non-aqueous ink provided with pseudoplasticity. The ink is provided by blending a non-Newtonian viscosity imparting and is provided with viscoelasticity by blending two types of polyvinyl pyrrolidone having different weight-average molecular weights to eliminate ink blobbing and scratching, and to a non-aqueous ball point pen using this ink.
A conventional non-aqueous ball point pen has been designed by setting an ink viscosity in a range of 10,000 to 30,000 mPaxc2x7s (20xc2x0 C.) to prevent leakage. However, when the viscosity during writing is high in this manner, the ball rotation resistance during writing automatically increases and writing smoothness was very low and fails to be satisfactory. Moreover, a high writing pressure was necessary during writing. In some cases, a load of 500 gf or more was applied to a pen point. The heavy load causes the pen point to be quickly damaged. Furthermore, ball breakage and writing defects frequently could occur as a consequence. On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 6-313143 (1994), 6-313144 (1994), 7-196972 (1995) or 9-48941 (1997), attempts were carried out to improve the above-described defects by creating inks having a pseudoplasticity viscosity property, where the ink viscosity is low when writing and where the ink viscosity is relatively high when writing is not performed. However, the attempts were not sufficient in enhancing the writing smoothness and completely preventing the leakage.
The present invention provides an ink which realizes a remarkably satisfactory writing smoothness, eliminates blobbing and feathering and which can completely prevent leakage, and further provides a non-aqueous ball point pen in which during ink transport by way of writing, no ink adheres to an ink reserving tube inner wall and an ink residual amount is clear. xe2x80x9cBlobbingxe2x80x9d is a phenomenon in which a surplus ink during writing is accumulated in a pen point. xe2x80x9cFeatheringxe2x80x9d is blurring of the ink due to absorption by paper etc.
The present invention relates to a non-aqueous ball point pen ink which contains, as main components, a colorant, an organic solvent, a non-Newtonian viscosity imparting agent, and a total of 0.4 to 0.8 mass % of polyvinyl pyrrolidone, where 0.2 to 0.6 mass % of polyvinyl pyrrolidone has a weight-average molecular weight of about 1,000,000 to 1,500,000 and 0.1 to 0.4 mass % of polyvinyl pyrrolidone with a weight-average molecular weight of about 2,500,000 to 3,000,000. A non-Newtonian viscosity index of the ink may be in a range of 0.4 to 0.7, a viscosity in a shearing speed of 500 secxe2x88x921 is in a range of 3,000 to 6,000 mPaxc2x7s (20xc2x0 C.), and the viscosity in the shearing speed of 0.19 secxe2x88x921 may be in a range of 20,000 to 60,000 mPaxc2x7s (20xc2x0 C.). The non-Newtonian viscosity imparting agent may be a fatty acid amide wax with a melting temperature of 140xc2x0 C. or more. The non-Newtonian viscosity imparting agent may be fatty acid amide wax. The blend amount of the fatty acid amide wax may be in a range of 1.0 to 2.0 mass %.
The non-aqueous ink above can be directly filled into an ink reserving tube of a ball point pen. The ink reserving tube can be a polypropylene tube. An inner wall of the ink reserving tube can be treated with silicone.
According to the present invention, there is provided an ink in which an ink viscosity in a shearing speed of 500 secxe2x88x921 can preferably be in a range of 3,000 to 6,000 mPaxc2x7s. When the ink viscosity is less than 3,000 mPaxc2x7s, writing smoothness is satisfactory but drawn line blobbing can be remarkable, further feathering can be unsatisfactory, even though it is still acceptable. Moreover, when the viscosity exceeds 6,000 mPaxc2x7s, a low writing pressure and smooth stroke as the object of the present invention can be hardly embodied, even though it is still acceptable.
As a result of intensive studies on the writing stroke of a ball point pen, the present inventors found that the stroke largely depends on the ball rotation resistance during writing. As a result of experiments, when the ink viscosity in the shearing speed of 500 secxe2x88x921 is less than 1,000 mPaxc2x7s, the ball rotation resistance is remarkably reduced, but a boundary lubrication area is constituted without forming an ink oil film between a ball and a ball seat and the intrinsic smoothness of the non-aqueous ball point pen is deteriorated. Moreover, when the viscosity exceeds 10,000 mPaxc2x7s, the ball rotation resistance tends to increase and the stroke obviously tends to become heavy. Specifically, when the ink viscosity is in a range of 1,000 to 10,000 mPaxc2x7s, the stroke becomes satisfactory. However, to prevent feathering and blobbing, and embody the intrinsic deep drawn line of the non-aqueous ball point pen, the ink viscosity should preferably be 3,000 mPaxc2x7s or more at minimum. Furthermore, not only to pursue touch smoothness, but also to enable a low pressure writing of about 100 gf like an aqueous ball point pen, the ink viscosity should preferably be 6,000 mPaxc2x7s or less. The ink viscosity described herein was measured in a measurement environment of 20xc2x0 C. using a rheometer CSL manufactured by British Carrymay, Ltd.
Moreover, in the present invention, a non-Newtonian viscosity imparting agent is blended into an ink composition, and an ink non-Newtonian viscosity index is set to 0.4 to 0.7. As described above, to obtain the satisfactory stroke, the ink viscosity during writing, that is, during high shearing is set to be low. A likelihood of occurrence of leakage necessarily increases, and this cannot be prevented by a conventional ink design. To prevent this defect, pseudoplasticity is set as an ink viscosity property by containing the non-Newtonian viscosity imparting agent in the ink composition, and the ink viscosity when the ball point pen is not being used is set to be as high as possible. Moreover, adequate consideration was given also to the drawn line blobbing in the study of the ink viscosity, but it is also a fact that the drawn line blobbing is in an increase direction when the viscosity is set to be low. It is particularly mentioned that when the pseudoplasticity is set as the ink viscosity property, the cohesive force of the ink itself increases, the generation of a surplus ink in a pen point is reduced and an effect of eliminating the blobbing is brought about. When the non-Newtonian viscosity index is less than 0.4, the cohesive force of the ink itself excessively increases, an ink follow-up defect is caused, and a phenomenon of discontinuity, line cut and non-uniformity in line darkness (xe2x80x9cscratchingxe2x80x9d). On the other hand, when the index exceeds 0.7, the cohesive force decreases and the effect of preventing the blobbing is weakened.
The non-Newtonian viscosity imparting agent for use in the non-aqueous ink includes a fatty acid amide wax and a derivative thereof, linear chain fatty acid ester polymer, polyethylene oxide, hardened castor oil, organic bentonite, silica, sulfate-based anion activator, and the like, but the fatty acid amide wax is preferable considering from stability. Further considering from the stability during the high-temperature preservation of the ball point pen, it is most preferable to select the fatty acid amide wax with a melting temperature of 140xc2x0 C. or more as the non-Newtonian viscosity imparting agent. The amount of the fatty acid amide wax is in a range of 1.0 to 2.0 mass % in order to realize the non-Newtonian viscosity index of 0.4 to 0.7. The non-Newtonian viscosity index described herein was measured using the rheometer CSL manufactured by British Carrymay, Ltd. in a measurement environment of 20xc2x0 C. with appropriate values of angle and diameter of a cone plate in a shearing speed range of 1 to 600 secxe2x88x921.
Furthermore, in the present invention, the viscosity in a shearing speed of 0.19 secxe2x88x921 was set to a range of 20,000 to 60,000 mPaxc2x7s. By providing the ink viscosity property with the pseudoplasticity, the leakage could be minimized, but the ink viscosity during writing needs to be set to be low to obtain a satisfactory stroke, and it was therefore difficult to completely prevent the leakage of various ball point pen inks only by imparting the pseudoplasticity. The inventors have found that the viscosity in the shearing speed of 0.19 secxe2x88x921 needed to be 20,000 mPaxc2x7s or more to completely prevent the leakage, even though the viscosity lower than that amount was still acceptable. Moreover, when the viscosity in the shearing speed of 0.19 secxe2x88x921 exceeds 60,000 mPaxc2x7s, the ink fluidity tended to be lowered, the ink follow-up property during writing tended to be deteriorated, and the ink became inappropriate as a writing utensil ink. Examples of an ink viscosity adjuster include phenol resin, amide resin, xylene resin, hydro-rosin resin, ketone resin, and the like, and the adjuster is also effective as a fixer of a drawn line to a paper surface. The ink viscosity described herein was also measured using the rheometer CSL manufactured by British Carrymay, Ltd. in the measurement environment of 20xc2x0 C. The present invention realizes a remarkably smooth touch, embodies a non-aqueous ball point pen ink with which the low pressure writing is possible like the aqueous ball point pen, and provides an ink sufficient for simultaneously preventing the blobbing and leakage. Specifically, the ink viscosity in the shearing speed of 500 secxe2x88x921 is set to a range of 3,000 to 6,000 mPaxc2x7s (20xc2x0 C.) in order to obtain a satisfactory touch, and the ink viscosity property is provided with the pseudoplasticity in order to completely prevent the feathering and blobbing which would normally tend to increase because of the low ink viscosity setting. Furthermore, in order to satisfy the ink leakage preventing performance and ink follow-up property which become insufficient when the ink is applied to various ball point pens, the viscosity in the shearing speed of 0.19 secxe2x88x921 is set to a range of 20,000 to 60,000 mPaxc2x7s (20xc2x0 C.).
Furthermore, the inventors thoroughly analyzed the relation between scratching and blobbing to embody a remarkably superior ball point pen performance. In the conventional non-aqueous ball point pen, a deep drawn line is obtained by interposing a pen point ball and transferring an ink film to a paper surface. In this case, as described above, the generation of the surplus ink, that is, the blobbing is prevented by the favorable viscoelasticity of the ink itself. On the other hand, when the viscoelasticity is too strong, the ink follow-up defect is caused as described above, and no smooth ink film can be formed on the pen point ball surface. This phenomenon is a scratching phenomenon. Specifically, the blobbing performance is a phenomenon contrary to scratching, and it is remarkably difficult to simultaneously enhance both performances.
The inventors empirically found that this difficult problem could be solved by simultaneously using resins having different properties in the ink components. It is necessary to provide the ink performance with viscoelasticity and select the resin which fails to deteriorate the ink stability, and polyvinyl pyrrolidone is optimum. Although the resins need to be different in properties as described above, there is a danger that completely different types of resins react in the ink. In this respect, for polyvinyl pyrrolidone, various grades different in molecular weights are extensively known and polyvinyl pyrrolidone can safely be employed in the ink. When polyvinyl pyrrolidone with a weight-average molecular weight of about 1,000,000 to 1,500,000 is added, the viscoelastic action is slightly insufficient, but the smooth ink film can easily be formed on the pen point ball surface, and a stable drawn line can be realized. Moreover, polyvinyl pyrrolidone with a weight-average molecular weight of about 2,500,000 to 3,000,000 provides a remarkably high viscoelasticity, and is effective for preventing the blobbing. By simultaneously using polyvinyl pyrrolidone compounds having different in properties, both the blobbing and scratching performances contrary to each other are enhanced.
The effect of polyvinyl pyrrolidone as the additive for providing the ink with the viscoelasticity has been reported, but the action of effectively facilitating the forming of the ink film with respect to the pen point ball is not known.
The total addition amount of polyvinyl pyrrolidone needs to be in a range of 0.4 to 0.8 mass % with respect to the total ink composition. When the amount is less than 0.4 mass %, the ink can be deficient in its viscoelasticity and the blobbing performance can hardly be sufficient. Moreover, when the amount exceeds 0.8 mass %, the viscoelasticity can be too strong, and scratching can result. For the blend ratio of polyvinyl pyrrolidone, an empirically obtained combination of 0.2 to 0.6 mass % of polyvinyl pyrrolidone with a weight-average molecular weight of about 1,000,000 to 1,500,000 and 0.1 to 0.4 mass % of polyvinyl pyrrolidone with a weight-average molecular weight of about 2,500,000 to 3,000,000 is most effective.
When the blend amount of polyvinyl pyrrolidone with the weight-average molecular weight of about 1,000,000 to 1,500,000 is less than 0.2 mass %, or when the blend amount of polyvinyl pyrrolidone with the weight-average molecular weight of about 2,500,000 to 3,000,000 is less than 0.1 mass %, the ink is deficient in its viscoelasticity and the blobbing performance cannot be enhanced. Moreover, when the blend amount of polyvinyl pyrrolidone with the weight-average molecular weight of about 1,000,000 to 1,500,000 exceeds 0.6 mass %, or when the blend amount of polyvinyl pyrrolidone with the weight-average molecular weight of about 2,500,000 to 3,000,000 exceeds 0.4 mass %, the viscoelasticity is too strong, and scratching results. The total blend amount of polyvinyl pyrrolidone needs to be in a range of 0.4 to 0.8 mass % with respect to the total ink composition. With the amount of less than 0.4 mass %, even when polyvinyl pyrrolidone with the weight-average molecular weight of 2,500,000 to 3,000,000 is used, the ink can be deficient in its viscoelasticity and the blobbing performance cannot be enhanced.
As polyvinyl pyrrolidone with the weight-average molecular weight of about 1,000,000 to 1,500,000, PVP K-90 (manufactured by GAF, Ltd., weight-average molecular weight of 1,280,000) is exemplified, and as polyvinyl pyrrolidone with the weight-average molecular weight of about 2,500,000 to 3,000,000, PVP K-120 (manufactured by GAF, Ltd., weight-average molecular weight of 2,800,000) is exemplified.
A colorant as the essential component of the present invention can be used without being particularly limited to the dye or pigment heretofore employed in the non-aqueous ball point pen. Examples of the pigment include organic, inorganic and processed pigments, such as carbon black, phthalocyanine, azo, quinacridone, anthraquinone, and indigo pigments. Moreover, as the dye, an alcohol-soluble dye, oil-soluble dye, direct dye, acid dye, basic dye, metallized dye, and various salt-forming type dyes can be employed. Moreover, these can be used alone or as a mixture. The blend proportion is preferably in a range of 5 to 50 mass % with respect to the total ink composition.
The organic solvent for use in the present invention is used as an ink composition solvent, or dispersing medium. Concretely, alcohol and glycol solvents such as benzyl alcohol, propylene glycol and butylene glycol, Cellosolve solvents such as phenyl Cellosolve, Carbitol solvents such as phenyl Carbitol, and nitrogen-containing solvents such as N-methyl pyrrolidone can be used alone or as a mixture. The blend proportion is preferably in a range of 30 to 70 mass % with respect to the total ink composition.
Here, a ball point pen structure will be described. For an ink reserving tube for the non-aqueous ball point pen, usable materials are limited from the standpoints of chemical resistance, moisture permeability, air permeability, and the like. In this respect, it has heretofore been most general to use polypropylene as the material. However, in the present invention particularly when the fatty acid amide wax is selected as the non-Newtonian viscosity imparting agent, the fatty acid amide wax has a very strong affinity for polypropylene. Therefore, when the ink is transferred from the ink reserving tube, a defect is generated that the ink adheres to the inner wall and the ink residual amount fails to be clarified. As a countermeasure against the defect, the present inventors have found that when the ink reserving tube is formed of polypropylene, the ink reserving tube inner wall is to be treated with silicone. When silicone is applied to the ink reserving tube inner wall, polypropylene as the reserving tube material does not directly contact the ink and keeps a relation that silicone is interposed, so that during the movement of the ink, the prevention of adherence to the reserving tube inner wall is embodied. As a silicone material, TSF-4420 (Toshiba Silicone Co., Ltd.) is exemplified. It is a most effective application method to simultaneously and uniformly apply silicone to the inner wall during extrusion molding.
When a tube of polyethylene terephthalate or nylon is used as the ink reserving tube, the application of silicone is not necessarily required.